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3.2. ORIGINS OF BIODIVERSITY (Natural selection (within a population of…
3.2. ORIGINS OF BIODIVERSITY
Knowledge and Understanding
Evolution - gradual change in genetic character of populations over many generations - achieved primarily through the mechanism of natural selction
Environmental change - challenges to species which drives evolution of diversity
There have been major mass extinction events in the past
Biodiversity ariises from evolutionary processes
Biological variation arises randomly and can either be beneficial, damaging or have no impact on the survival of the individual
Natural selection
within a population of one species there is genetic diversity, which is called variation
due to natural variation, some individual will be fitter than others
fitter individuals have an advantage and will reproduce more successfully
offspring of fitter individuals may inherit the genes that give the advantage
contribute to evolution of biodiversity overtime
over many generations if a population is separated from others and isolated, differences may increase to such an extent that if reunited they can no longer interbreed - then a new species is formed and speciation has occured
Physical barriers
Species can develop into two or more new species if their populations split by some kind of physical barrier e.g. a mountain range
Physical barriers split the gene pool - so genes on both sides of the barrier no longer mix making it possible for the two populations to develop in different directions
example of speciation due to physical barriers - large flightless birds,
Land bridges
allows species to invade new areas e.g. N and S America were separated for a long time and therefore have rather different species
geological land bridge of central America is recent and has allowed species to move to the north and the south e.g. bears moved from north to south America
land bridges may result from lowering of seawater levels instead of continental drift e.g. now disappeared land bridge between UK and Europe
Continental drift
continents have moved to different climate zones - changing climatic conditions and therefore food supplies forced adaptation in species and resulted in increased biodiversity
e.g. antarctica
Mass extinctions
background extinction rate - between 10 and 100 species extinct per year
due to rapid change in climate, natural disaster e.g. volcanic eruption - there have been 5 mass extinctions in the past
currently the 6th mass extinction? - mammals background rate = 1 per 200 years - last 400 years has been 89
many are also living dead species (species with such small population it is unlikely they will survive)
mostly species that can survive in human urban environments e.g. rats or domesticated animals are likely to survive the 6th mass extinction
Living planet index - WWF - reports trends in Earth's biological diversity